The present invention relates to devices and method for measuring mass flow rates of fluids, such as liquids and gases.
Devices and methods of the above mentioned general type are known in the art. One of the known vibration devices for measuring mass flow rates is disclosed for example in U.S. Pat. No. 4,096,746 and operates on the basis of measurement of Coriolis forces, which are generated during vibrations of a console-type mounted part of a pipeline.
Vibration mass flow rate meters which are provided with two U-shaped pipes are disclosed in U.S. Pat. No. 4,491,025. The pipes are mounted in a rigid housing and the device is provided with a unit for exciting vibrations and adapters for receiving signals from the vibrating pipes, both arranged on the pipes. An electronic block measures a difference of phases in time units between voltages on the adapters and indicates a mass flow rate in corresponding units.
Mass force (Coriolis force) flow rate meters are also known in particular for measurements of a flow rate of two-phase mediums. They are disclosed for example in publication P. P. KREMLEVSKY. “Flow Rate Meters and Quantity Counters”, L, “Machine Building”, 1989, pp. 636-637.
Also, vibration mass flow rate measuring devices are known, which have a housing with the U-shaped pipes and the vibration excitation unit and adapter units located on the pipes, which provide correction of mass flow rate of liquids with gas and other inclusions, based on preservation of value of a flow rate during obtaining of a signal-change of density and/or voltage on the excitation unit, as disclosed in Hanus Henry, “Self-Validating Digital Coriolis Mass Flow Meter”, Computing Engineering Journal, October 2000, and Rota MASS 3 Series Coriolis—Mass Flowmeter. Instruction Manual, 2010.
The U-shaped pipes, under the action of the excitation unit, perform vibrations with own frequency in a counter phase. During this process Coriolis acceleration is generated in the liquid which moves in the pipes (proportionally to a product of transmission speed of liquid and liquid speed) and corresponding forces which act on the pipes. These forces lead to generation of a phase difference on the adapters, which is proportional to the mass flow rate. When the liquid contains gaseous or other inclusions with density that is different from density of the liquid, not whole mass of liquid and inclusions takes part in transitional movement (caused by vibrations of the pipe). In other words, contrary to single phase liquid, transitional speeds of different phases (inclusions) will be different, which is known as “phase sliding”). A summarized transitional speed of liquid and inclusions will be lower than a speed of a homogenous liquid, and therefore Coriolis acceleration, phase difference and indicated mass flow rate will be lower. In other words a negative error of flow rate measurement occurs.
Correction of the error of flow rate is carried out by preservation of value of flow rate from a moment of appearance of gaseous and other inclusions to a moment of restoring homogeneity of liquid. A signal for turning on and turning of a correction is a change of density and voltage at the excitation unit. Thereby the error of flow rate measurements in presence of (short-term) gaseous and other inclusions is reduced.
The above described correction is however possible only in the case of short-term influence of inclusions in liquid. It also does not take into consideration a possibility of real reduction of mass flow rate in presence of gaseous inclusions due to increase of hydraulic resistance. Finally, instability of “zero” point of correction function, because a mode of a homogenous liquid is rare while a mode with more or less inclusions is more often, can lead to significant errors in correction of a mass flow rate